Add sample IAM policy

[epicfaace]

This is so that users who don't use WP CLI can still create an IAM policy with the appropriate permissions.

[hm-linter]

Linting failed (1058 errors, 83 warnings).

1141 notices occurred in your codebase, but none on files/lines included in this PR.

[codecov-io]

Codecov Report

Merging #265 into master will decrease coverage by 37.2%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #265       +/-   ##
============================================
- Coverage     46.43%   9.23%   -37.21%     
  Complexity      260     260               
============================================
  Files             7       7               
  Lines           715     715               
============================================
- Hits            332      66      -266     
- Misses          383     649      +266

Impacted Files	Coverage Δ	Complexity Δ
inc/class-s3-uploads-stream-wrapper.php	2.17% <0%> (-55.44%)	149% <0%> (ø)
inc/class-s3-uploads.php	23.72% <0%> (-51.7%)	44% <0%> (ø)
inc/class-s3-uploads-image-editor-imagick.php	60% <0%> (-2.86%)	9% <0%> (ø)

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[joehoyle]

Thanks @epicfaace , apologies for not getting to this ever. We've since updated the policy (see https://github.com/humanmade/S3-Uploads/blob/master/inc/class-wp-cli-command.php#L72-L103) so this would need updating.